Fail-safe probe-type thermostatic control device



May 19, 1964 E. G. THEM 3,134,003

TAIL-SAFE PROBE-TYPE 'IHERMOSTATIC CONTROL DEVICE Filed Feb. 17, 1961 2 Shuts-Shoat 1 FIG. I

8/ INVENTOR. EDWARD 6. THEN ATTORNEY May 19, 1964 a s. THEM 3,134,093

TAIL-SAFE PROBE-TYPE msmos'mnc CONTROL navzcs Filed Feb. 17, 1961 2 Sheets-Sheet 2 mmrrox. EDWARD s. 'rugm ATTORNEY l 3,134,003 FAIL-SAFE PROBE-TYPE THERMOSTATIC CONTROL DEVICE Edward G. Them, Mansfield, Ohio, asslgnor to Therm-O- Disc Incorporated, Mansfield, Ohio, a corporation of Ohio Filed Feb, 17, 1961, Ser. No. 90,021

g r 4 Claims. (Cl. 200--137) This invention relates to an improved heat responsive switch, and more particularly to switch actuating means embodying a heat sensing probe member adapted to be positioned in the fuel flame of a heating appliance such as furnaces, ranges, and clothes driers.

Various types of switches have been proposed heretofore which are intended to operate inresponse to the presence or absence of a gas flame in heating appliances such as furnaces, cooking ranges or ovens, and clothes driers. Such switches have embodied many undesirable features and drawbacks, and through failure have proved to be unsafe for domestic use as asafety device in such appliances. For example, in devices in which a probe has been used as a flame sensing element, after extended periods of exposure to the flame, the probe will deteriorate and disintegrate or break, and thus fail to actuate the switch in the electric circuit to the valve controlling the flow of gas to the appliance. In other cases, the probe will change in physical character to the extent that the switch will fail to operate within a predetermined prescribed period of time or within desired temperature limits. In devices using bimetal as a flame sensing element, over-stress and deteriorationofthe bimetal is effective to cause failure of the-switch actuating elements of the device or to cause the switch to operate within unsafe limits.

It is among the objects of the present invention to provide a new and novel temperature sensing device for actuating a switch controlling the electric circuit to an electrically operated'fuel valve which is adapted to interrupt or open said electric circuit on the absence or removal of a flame impinging on the sensing device or a substantial drop in the temperature surrounding the same.

Another object of the present invention is to provide a switch actuatingdevice which will operate within fixed limits of time or temperature regardless of physical changes: in the character of the flame sensing element upon extended periods of exposure to a flame.

A still further object of the invention is'to provide'a switch for controlling the flow of current to an electrically' operated fuel valve which is actuated by a flame sensing element, wherein the switch elements are caused to open or close in the event of failure of the flame sensing element.

It is a still further object of the invention to provide a switch for a heating applicance which because of its simplicity, economy of construction, and reliability and efliciency of operation'is particularly well adapted as a protective device in controlling the circuit to the fuel valve to such heating appliance.

Another object of the invention is to provide a probe type flame sensing element for a switch wherein relative movement of the members of the sensing element are coordinated with the spacing of the contact elements of the switch so that the former is positive in switch actuating movement within predetermined limits.

These and other objects and advantageous features of the invention, not at this time more particularly pointed out, will become apparent asthe nature of the invention is better understood from the following detailed description taken in conjunction with the accompanying drawing, wherein. like reference characters denote corresponding parts and wherein:

FIGURE 1 is a top plan view of a device made in w cordance with the present invention,

FIGURE 2is a longitudinal sectional view of the device of FIGURE 1 with the switch contacts shown in normally open position,

FIGURE 3 is a'ventical sectional view taken along the line 3-3 of FIGURE 2, centrally through the switch mechanism,

FIGURE 4 is a sectional 4-4 of FIGURE 2,

FIGURE 5 is a sectional view taken along the line 5-5 of FIGURE 2.

view taken along the line With reference to FIGURES 1 and 2 of the drawing,

is adapted to either engage or disengage fromthe fixed contact, a flame sensitive assembly B, and a movement limiting element 0 which coordinates the movement of the elements of assembly B in response to the presence or absence of a flame projecting onthe latter or the influence of substantial temperature changes thereon. In accordance with the present invention the switch proper A and the temperature sensing assembly 13 in themselves are of conventional construction. The elements of C coordinating the movement of the elements of assembly B to actuate the contact elements of switch A constitute a novel and improved arrangement for translating the movement which takes place in the assembly B in response to the absence of a flame within the chamber surrounding assembly B and for imparting such movement for positive action of the switch proper;

The switch proper A which, as stated, is of conventional construction, is embodied within a housing 10 Y which may be of suitable insulating material, although withstand extremely high temperatures, such being the case when the switch would be placed in close proximity to either the pilot flame or main burner of the heating appliance. The housing 10 is generally cup-shaped, having a closed upper end as shown in FIGURES 1, 2' and}, and at its lower end presenting a laterally outwardly protruding peripheral flange 11. As shown in FIGURES 2 and 3, the housing 10 presents a generally cylindrical downwardly facing switch chamber 12. A separate end wall or shield 13 of suitable insulation material, extends across the lower end of the housing 10, providing a closure for the lower end of the switch chamber 12. This lower end wall 13 has a reduced diameter central portion 13a. which projects up into the chamber 12 and has a snug fit therein against the interior side wall of the housing 10. l

.The switch housing 10 and the bottom endwall 13, therefore, are supported by a cup-shaped metal'case 14.

As shown in FIGURES 2 and 3 this metal case has its bottom wall 15 secured to a metal mounting bracket 16 which is adapted to be assembled on the appliance with which the device is used and may take any suitable form varying with the application. The metal case 14 presents a generally cylindrical side wall 17 which extends upward ly from the bottom wall 15 and terminates in a laterally inturned flange 19 which snugly overlies the peripherally upwardly facing shoulder of the flange 11 on the switch housing 10. Between its outurned wall portion 18 and its inturned flange 19, the metal case 14 snugly engages the respective peripheries of flange 11 of the switch housing 10, and the bottom wall 13 for the housing. A stationary switch contact member 20 presents an upwardly facing, rounded contact surface '21 inside the switch chamber 12. This stationary contact member extends laterally across the upper side of the top of the closure member 13 and has an upwardly extending stem 22 tom wall 13 of the switch case.

which projects up through the housing wall for connection to a terminal 23 disposed on the outside of the switch housing.

A movable contact carrying arm 24 carries a downwardly facing mobile contact 25 which engages the stationary contact 20 when the movable contact arm is in the position shown in FIGURE 3. As best seen in FIG- URE 5, this movable contact arm 24 is a generally flat, resilientmetal leaf which is approximately T-shaped in outline. .The contact arm- 24 is cantilever mounted at one end by means of a rivet 26 which extends up through the A rigid metal spacer end of the contact-carrying arm 24 and the top wall of the housing 10. The enlarged head on the rivet engages the bottom face of the contact-carrying arm 24 and its cantilever-mounted end and holds it lightly up against the spacer 26b. Along the inner edge of its cantilevermounted end, the contact-carrying arm 24 is formed with a bend as at 28, so that beyond its cantilever mounting the contact arm is biased downwardly at a slight angle when in its unstressed position, as is best shown in FIGURE 2.

For operating the contact-carrying arm 24, there is provided a bumper member 32 of suitable insulating material which has a rounded upper end adapted to engage beneath the contact-carrying arm 24 at the center thereof, as will be best seen in FIGURES 2 and 3. This bumper member 32 is slidably received loosely in a central opening 33 extending through the bottom wall 13 of the switch housing. The bumper member 32 has a fiat lower end which is disposed below the bottom wall 13 of the switch housing. The lower end of the bumper member 32 is positioned to be engaged and be actuated by the temperature sensing assembly -B of the present invention, as described hereinafter.

The temperature sensing assembly in the present invention' comprises an elongated tube 34 having a flanged upper end, which seats within a recess 35 formed in the mounting bracket 16. An elongated rod 37 is welded in the lower end of the tube 34 as at 36, and extends up wardly therefrom through the tube 34 in concentric relation with the tube. The rod 37 extends up loosely through a central bore 38 formed in the plate 39. The

plate 39 is secured on the inner face of the bottom wall of the casing by means of rivets 39a which extend through the casing wall and the mounting bracket 16. The flanged end of the tube 34 is thus securely clamped between the upper face of the mounting bracket and the outside surface of the bottom wall 15 of the case 14. The upper end of the rod 37 is disposed in the chamber 40 which is located inside the metal case 14 below the bot- Preferably the rod 37 is of a metal having a relatively low coeflicient of expansion, while the tube 34 may be of any suitable metal having an appreciably higher coefficient of expansion than the rod 37. With this arrangement which is a conventional structure of controls of this general design, when the temperature sensing assembly is heated the inner rod 37 will expand less than the outer tube 34, so that the upper end of the rod 37 will withdraw from within the chamber 39.

In accordance with the present'invention, the relative movement of the rod 37 with respect to the tube 34 is controlled by the assembly C and when such movement exceeds a predetermined amount the assembly C is effective to control the same, or if perchance the elements of assembly B become so deteriorated or separated, that the assembly fails to function normally, the assembly C will come into play to effectively actuate the contact of the switch A.

The assemblage C comprises an elongated threaded shank 43 formed on the upper end of the rod 37 and adapted to abut and engage the lower end surface of the bumper member 32. The opposite end of the bumper member 32 is engaged by the end of an adjusting member 44 which is threaded through a bearing member 45 secured to the upper face of the contact-carrying member 24. Adjustment of the member 44 within the bearing block 45 may be effected through an opening 46 formed in the upper surface of the wall of the housing 10. Any suitable tool may engage the slotted end of the member 44 for rotating the same within the member 45. A suitable closure member 47 is inserted in the opening 46 to seal the same. Threaded on the shank 43 of the rod 37 is an inverted cup-shaped bushing member 48, the lower peripheral edge 49 thereof being adapted to engage the upper surface of the plate 39 to effectively restrict the relative movement between the rod 37 and'tube 34. A lock nut 50 is also threaded on the shank 43 to secure the cup: shaped member 48 in adjusted position on the shank 43. Surrounding the rod 37 as it projects into the chamber 40 and within the cavity of the member 48 is a helical spring 51. One end of this spring 51 engageslthe uppersurface of the plate 39 and the other end engages and seatswithin the cavity of the member 48 and normally exerts an upward pressure thereon. The pressure exerted by, the spring 51 on the cup-shaped member 48 is suflicient to overcome any bias of the contact-carrying member 24" in the event that there'is any breakage between the rod 37 and tube 44 permitting the rod to move independently of the tube 34. Under such a condition, the assemblyCis effective to open the contacts 21 and 25 of the switch mechanism A and thus break the electric circuit to the valve actuating mechanism.

In the operation of the elements of the assembly C, as shown in FIGURE 2, the switch contacts and elements of assembly C are in the position shownunder normal room temperature. The spaced gap between the fixed contact 21 and the mobile contact 25 has been predeterminedand adjusted by means of the adjusting screw 44. The inverted cup-shaped bushing member 48 has been threaded on the shank 43 and moved down until the peripheral edge 49 thereof is in contact with the upper surface of the plate 39. The bushing member is then backed off to provide a predetermined spacing between the peripheral edge 49 and the upper surface of the plate 39 relative to the gap between the mobile contact 25 and the fixed conbling is inserted into the combustion chamber of a furnace so that the pilot flame of the device plays or impinges upon the assembly. When the assembly B is exposed to the flame of the pilot, the tube 34 will expand lengthwise downwardly as shown in FIGURE 2. Such downward movement of the tube 34 will withdraw the rod 37 within the chamber 40 relieving the pressure on the bumper 32 and the bias of the contact-carrying member 24 will bring the mobile contact 25 into engagement with the fixed contact 21 and close the circuit to the control valve. The movement of the rod will continue until the edge surface 49 of the cup-shaped bushing member 48 engages with the plate 39. Any further expansive movement of the tube 34 will effect a stretching of the rod, but will not be effective upon the assembly C or the elements of the switch member A. In the event that'the flame of the pilot, or the burner flame should be extinguished, the tube will contract and the end of the rod-will be effective against the bumper 32 to overcome the bias of the contact-carrying member 24 to separate the mobile contact from the fixed contact. In the normal use of heat sensing assemblies of this type, continual impingement on the tube 34 will be effective to change the physical character of the elements of the assembly such that, for example, there is a tendency due to what is known as carbon growth for the tube to be permanently elongated. Such elongation in the tube would be taken up in the stretching of the rod where it is restricted in its outward movement by the bushing member 48. Thus, there is always a relative movement upon the flame being removed from the tube or the temperature is substantially decreased in the area surrounding the tube and the contraction would be effective to cause the rod to project into the chamber 40 and separate the contacts.

In other instances, the continual impingement of a gas flame upon the tube causes-deterioration of the tube member and eventually brings about a condition where the tube and rod separate. Under such conditions, the spring member housed within the cup-shaped bushing member 48 is brought into play to exert pressure through the rod 37 against the bumper 32 and separate the mobile and fixed contacts of the switch A. Thus, upon the absence of a flame, or upon a breakage of the elements of the temperature sensing'assembly B. or the ineffectiveness of the elements thereof to close the switch, the assembly C is always effective to open the contacts of the switch mechanism.

that various modifications. omissions. and refinements which depart from the disclosed embodiment may be adopted without departing from the spirit of scope of this invention as defined in the appended claims.

I claim:

1. 'A heat sensitive control device comprising means de fining a hollow housing, a wall member separating said housing into first and second chambers, switch means mounted in said first chamber, a slidable member supported by said wall member for actuating said switch means,- a heat responsive probe having a tubular outer member and an actuating member contained therein operatively connected together, said actuating member proje cting into said second chamber and engageable with said slidable member and means in said second chamber on the end of said actuating member for adjustably limiting the relative movement between the said actuating and tubular members of said probe when the latter is subjected to high temperature, said last-named means effective upon separation of said members of the probe for actuating said slidable member.

2. A heat sensitive control device comprising means defining a hollow housing, a wall member separating said housing into first and second chambers. switch means mounted in said first chamber, a slidable member supported by said wall member or actuating said switch means, a heat responsive probe having a tubular outer member and an actuating member contained therein operatively connected together, said actuating member projecting into said second chamber and engageable with said slidable memben-and means on the end of said actuating member within said second chamber for preventing the withdrawal of the said actuating member from said second chamber beyond a predetermined 'fixed amount when said probe is subjected to high temperature, said last-named means effective upon separation of said members of the probe for actuating said slidable member.

3. A heat sensitive control device comprising means defining a hollow housing, switch means mounted in said housing, including a stationary contact, a mobile contact for engagement with said stationary contact and a. movable contact-carrying arm which carries the mobile contact, a heat responsive probe having an elongated tubular member and a rod within said tubular-member operativelyconnected thereto and projecting into said housing for actuating said movable contact-carrying arm, and means on the free end of said rod for 'adjustably limiting the movement of said rod away from said contact-carrying arm when the probe, is subjected to a tem perature beyond a predetermined fixed amount and for moving said rod toward said contact-carrying arm to open the contacts when the members of said probe become separated.

4. A heat sensitive control device comprising means defining a hollow housing, switch means mounted in said housing having a stationary contact, a mobile contact for engagement with said stationary contact, a movable contact-carrying arm supporting said mobile contact biased in one direction, and a heat responsive probe spaced from said contact-carrying arm including an outer tubular member and an inner actuating member connected to said tubular member movable toward and away from said contact-carrying arm in response to heat changes, means mounted on said actuating member for adjustably limiting the movement of the said actuating member when the probe is subjected to a temperature beyond a predetermined fixed amount and after engagement of said mobile contact with said stationary contact, and spring means for moving said actuating member to open said contacts when the said actuating and, tubular members of the probe become separated.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain July 16,

ERNEST W. SWIDER Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 134,003

' Edward G. Them It is hereby certified that error appears in the above numbered petent 'requiringeorrection and that the said Letters Patent should read as corrected below.

In the heeding to the drawings,

Sheets 1 and 2 line 2, title of invention for "TAIL-SAFE" read FAIL-SAFE Signed and seled this 22nd day of September 1964.,

(SEAL) Anest:

EDWARD J. BRENNER Commissioner of Patents May 19, 1964 

1. A HEAT SENSITIVE CONTROL DEVICE COMPRISING MEANS DEFINING A HOLLOW HOUSING, A WALL MEMBER SEPARATING SAID HOUSING INTO FIRST AND SECOND CHAMBERS, SWITCH MEANS MOUNTED IN SAID FIRST CHAMBER, A SLIDABLE MEMBER SUPPORTED BY SAID WALL MEMBER FOR ACTUATING SAID SWITCH MEANS, A HEAT RESPONSIVE PROBE HAVING A TUBULAR OUTER MEMBER AND AN ACTUATING MEMBER CONTAINED THEREIN OPERATIVELY CONNECTED TOGETHER, SAID ACTUATING MEMBER PROJECTING INTO SAID SECOND CHAMBER AND ENGAGEABLE WITH SAID SLIDABLE MEMBER AND MEANS IN SAID SECOND CHAMBER ON THE END OF SAID ACTUATING MEMBER FOR ADJUSTABLY LIMITING THE RELATIVE MOVEMENT BETWEEN THE SAID ACTUATING AND TUBULAR MEMBERS OF SAID PROBE WHEN THE LATTER IS SUBJECTED TO HIGH TEMPERATURE, SAID LAST-NAMED MEANS EFFECTIVE UPON SEPARATION OF SAID MEMBERS OF THE PROBE FOR ACTUATING SAID SLIDABLE MEMBER. 